Multi-stage spring band air preheater



June 15, 1965 F. FIKEN SCHER MULTI-STAGE SPRING BAND AIR PREHEATER 2 Sheets-Sheet 1 Filed Aug. 10, 1962 FIG.|.

FLUE GAS AIR TO BE HEATED INVENTOR FRIEDRICH FIKENSCHER June 1 Filed Aug. 10, 1962 MULTI-STAGE SPRING BAND AIR- PREHEATER FIG.2.

2 Sheets-Sheet 2 TEMPERATURE CURVE OF THE FLUE GAS AND OF THE COMBUSTION AIR TEMPERATURE OF THE FLUE GAS TEMPERATURE STEP CAUSED BY zINTERPOSED COOLING DEVICE TEMPERATURE OF I THE COMBUSTION AIR L HOT STAGE COLD STAGE I AMOUNT OF HEAT P INTERCHANGED BETWEEN FLUE GAS AND COMBUSTION AIR FRIEDRICH FIKENSCHER INVENTOR United States Patent 3,189,1283 MULTLSTAQE SERENG BAND AER PREHEATER Friedrich Fiirenscher, Gnrnmershach, Rhineiand, Germany, assignor to L. dz C. Steinnriiiier G.rn.b. -i., Gummersbach, Rhineiand, Germany Filed Aug. m, 1962, Ser. No. 217,255 2 Ciairns. (Qi. res- 7 The present invention relates to a multistage spring band air preheater. For purposes of heat exchange from hot flowing gases to cold gases, heat exchangers have become known which operate with an endless spring band extending successively through both gas passages. With such an arrangement, the spring band is by means of rollers, passed back and forth in both passages transverse to the longitudinal direction of the band and, at the hot end, passes from the heating gas passage into the passage of the gas to be heated, and at the cold end passes from the passage of the gas to be heated into the heating gas passage. By driving a portion of the rollers, the spring band is in continuous movement. Consequently, the said spring band or spring belt is heated in the heating gas passage up to a temperature which is only slightly less than the entrance temperature of the hot gases, whereas said band or belt is cooled in the passage of the cold gas to approximately the entrance temperature of the cold gas.

Such a device may also be employed for preheating the combustion air in boiler installations by outflowing flue gases. In this connection, however, there exists the dificulty that the temperature curves of the available flue gas and the temperature curves of the air to be heated intersect, which means that without the employment of special means, either the air is not heated up to the highest possible temperature in the neighborhood of the gas entrance temperature, or the flue gas cannot be cooled to the desired lowest temperature. In order to overcome these diiliculties, it has been suggested to subdivide that portion of the installation which is passed through by the flue gases, into two stages and to feed a portion or" the flue gas into the cold stage while bypassing the hot stage. In this way, the hot stage is passed through by a smaller quantity of gas than the cold stage. Such an arrangement, however, requires additional bypass conduits for that portion of the gas which gives off heat and which is added only later. Moreover, a further drawback of this arrangement consists in that in view of the different quantities of the gases passing through, either the passage cross-sections have to be made smaller in the hot stage, or the speed of flow has to be reduced.

It is, therefore, an object of the present invention to overcome the above mentioned drawbacks.

It is a further object of this invention to provide a multi-stage spring band air preheater in which the heat transmitting spring band or spring belt will from the zone of the entrance temperature of the second stage suddenly pass into the zone of the exit temperature of the first stage without having absorbed any material amount of heat.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing illustrating a spring band air preheater according to the present invention.

FIG. 1 shows a cross sectional view of the invention.

FIG. 2 shows a temperature curve of the flue gas and of the combustion air.

The arrangement according to the present invention is characterized primarily in that that portion of the installation which is passed through by the flue gas is sub-divided in two stages in a special way. More specifically, instead of having both stages passed through 3,189383 Patented June 15, 1965 by different quantities of a medium which gives off heat, according to the present invention, a cooling device is interposed between the hot stage and the cold stage, and this cooling device cools off the gas, which leaves the first stage, to a lower temperature. In this way, in the temperature curve of the flue gas there will, between the two stages, be formed a step which makes it possible to heat up the air in a steady manner up to a temperature which is close to the entrance temperature of the flue gas. This cooling device may advantageously employ, as a cooling system, feed water taken ofi from a suitable point in the feed water preheater system and then, thereafter, returned to the system.

According to a practical embodiment of the invention, the spring band or spring belt may, for a certain distance, be passed along the longitudinal wall of the flue gas passage, and feed water preheater elements may be built into the thus created space between the spring belt windings. With such an arrangement, the heat transmitting spring band or spring belt passes from the zone of the entrance temperature of the second stage suddenly into the zone of the exit temperature of the first stage without having absorbed any material quantity of heat.

According to a second embodiment of the invention, instead or" one spring band or spring belt, two endless spring bands or spring belts are employed. One of these spring belts comprises the lower temperature stage only, whereas the second spring belt extends only over the upper temperature stage. In this instance, when comparing the temperature curve of the air with the temperature curve of the flue gas, the distance between the two curves representing the temperature drop and steadily decreasing with the heating up of the air will, at that portion at which the step in the temperature curve of the flue gas is located, likewise and stepwise decrease while decreasing gradually further above.

Referring more specifically to the drawing, the arrangement shown therein comprises a passage 1 for the air to be heated and a passage 2 representing the flue gas passage. In each of the two passages there is provided a number of rollers 3 which guide an endless spring belt 4. In the air passage l, the spring belt is passed through the passage in uniform windings extending transverse to the direction of flow. The spring belt enters through an opening 5 in the wall in hot condition into the air pas sage i leaves the latter through an opening 15 from where it passes in cooled condition into the flue gas passage 2. The rollers 13 merely serve for guiding the spring belt when passing from one passage into the other passage.

While the band or belt moves in uniform windings through the entire passage, the flue gas passage is practically sub-divided into three sections 12, 22 and 32. The sections 12 and 32 respectively form the hot stage and the cold stage for the flue gas. The section 22 contains a feed water preheater 6 which latter comprises a distributor '7 at the bottom portion thereof, a collector 1'7 at the top portion of said preheater, and a number of adjacent pipe coils 16 interposed between the distributor and collector. The spring belt passes over said intermediate stage at 3 parallel to the wall of the flue gas passage 2.

During the operation, air passes into the air passage from the bottom portion thereof and leaves the same at the top portion of the air passage while uniformly heating up on the spring belt. The passage 2 is passed through by the flue gas in inverse direction. In the hot stage 12, the gas first gives off heat to the already heated spring belt, then passes through the feed water preheater of the intermediate stage, and when passing through the cold stage 32 of the flue gas passage, the gas gives ofl heat to the cold spring belt. Between the hot stage and one belt for the hot stage, and one belt for the cold stage while each of the last mentioned two belts has to be driven individually. In this way, there exists the possi bility of respectively driving the spring belts at speeds differing from each other, whereby also the heat transfer may be differentiated as far as the last mentioned two a belts are concerned.

It is, of course, to be undertsood that the present invention is by no mean-s, limited to the particular construction shown in the drawing but also comprises any modifications within the scope of the appended claims. a

What I claim is:

1. In combination in an air preheater: first conduit means for passing flue gas therethrough, second conduit means for passing air to be heated therethrough, flexible endless metallic belt means passing through said firstand second conduit means in succession, said belt means passing through a first section and a second section of said first conduit means along a closed serpentine pass, pipe means interposed between said first section and said second section for conveying cooling water through said first conduit means, said pipe means being located at that portion of said first conduit means at which the temperature curve of the cold stage of said belt means approaches the temperature curve of the air to a certain minimum extent, said belt m ans passing in a longitudinal direction of said first conduit means adjacent one side thereof to leave space in said first conduit means for said pipe means. A

2. An air preheater according to claim 1, in which said pipe means comprises a plurality of coils, a distributor means common to and connected to one end of said coils, and collector means common to and connected to the other end of said coils.

4/56 Scholl 1656 8/57 Fikeuscher 16514O CHARLES SUKALO, Primary Examiner. 

1. IN COMBINATION IN AN AIR PREHEATER: FIRST CONDUIT MEANS FOR PASSING FLUE GAS THERETHROUGH, SECOND CONDUIT MEANS FOR PASSING AIR TO BE HEATED THERETHROUGH, FLEXIBLE ENDLESS METALLIC BELT MEANS PASSING THROUGH SAID FIRST AND SECOND CONDUIT MEANS IN SUCCESSION, SAID BELT MEANS PASSING THROUGH A FIRST SECTION AND A SECOND SECTION OF SAID FIRST CONDUIT MEANS ALONG A CLOSED SERPENTINE PASS, PIPE MEANS INTERPOSED BETWEEN SAID FIRST SECTION AND SAID SECOND SECTION FOR CONVEYING COOLING WATER THROUGH SAID FIRST CONDUIT MEANS, SAID PIPE MEANS BEING LOCATED AT THAT PORTION OF SAID FIRST CONDUIT MEANS AT WHICH THE TEMPERATURE CURVE OF THE COLD STAE OF SAID BELT MEANS APPROACHES THE TEMPERATURE CURVE OF THE AIR TO A CERTAIN MINIMUM EXTENT, SAID BELT MEANS PASSING IN A LONGITUDINAL DIRECTION OF SAID FIRST CONDUIT MEANS ADJACENT ONE SIDE THEREOF TO LEAVE SPACE IN SAID FIRST CONDUIT MEANS FOR SAID PIPE MEANS. 